Fixed shutdown concurrency issues in FilePathWatcher.

content/common/file_path_watcher/file_path_watcher.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // This module provides a way to monitor a file or directory for changes.
 
 #ifndef CONTENT_COMMON_FILE_PATH_WATCHER_FILE_PATH_WATCHER_H_
 #define CONTENT_COMMON_FILE_PATH_WATCHER_FILE_PATH_WATCHER_H_
 #pragma once
 
@@ skipping 22 matching lines @@
   };
 
   FilePathWatcher();
   ~FilePathWatcher();
 
   // Register interest in any changes on |path|. OnPathChanged will be called
   // back for each change. Returns true on success. |loop| is only used
   // by the Mac implementation right now, and must be backed by a CFRunLoop
   // based MessagePump. This is usually going to be a MessageLoop of type
   // TYPE_UI.
+  // OnFilePathChanged() will be called on the same thread as Watch() is called,
+  // which should have a MessageLoop of TYPE_IO.
   bool Watch(const FilePath& path,
              Delegate* delegate,
              base::MessageLoopProxy* loop) WARN_UNUSED_RESULT;
 
   class PlatformDelegate;
 
   // Traits for PlatformDelegate, which must delete itself on the IO message
   // loop that Watch was called from.
   struct DeletePlatformDelegate {
     static void Destruct(const PlatformDelegate* delegate);
@@ skipping 37 matching lines @@
     scoped_refptr<base::MessageLoopProxy> message_loop_;
   };
 
  private:
   scoped_refptr<PlatformDelegate> impl_;
 
   DISALLOW_COPY_AND_ASSIGN(FilePathWatcher);
 };
 
 #endif  // CONTENT_COMMON_FILE_PATH_WATCHER_FILE_PATH_WATCHER_H_